L-Tryptophan
Supplements · Amino Acids · Supplement, Typed Supps
An essential amino acid your body can’t make itself — a real building block for serotonin and melatonin, with decent evidence for helping with sleep and a real safety history worth knowing about.
Stage by stage
- Intake (Capsule or dietary protein): Absorbed from the small intestine.
- Small intestine (Absorbed): Competes with other amino acids for the same transport system.
- Bloodstream (Circulates): Travels to the brain, competing again for blood-brain-barrier transport.
- Brain (Converted): Converted into serotonin, then melatonin.
What the evidence supports
- Improving sleep quality, particularly reducing time spent awake after sleep onset — moderate evidence. A systematic review and meta-analysis pooling multiple trials found tryptophan supplementation significantly reduced wake-after-sleep-onset time — a genuine, quantifiable sleep-architecture effect, though the number of pooled trials was still relatively small.
- Improving mood or reducing anxiety in healthy adults — limited evidence. Low blood tryptophan is associated with depression in observational data, and some trials in healthy adults using doses from 0.14–3 g/day report reduced anxiety and improved mood, but this evidence is less consistent and robust than the sleep data.
- Evidence on Risk of serotonin syndrome when combined with serotonergic medications — strong evidence. This is a well-recognized, mechanistically clear interaction — combining tryptophan with SSRIs, SNRIs, MAOIs, or other serotonergic drugs raises real risk and should be avoided without medical guidance.
- Evidence on Historical link to eosinophilia-myalgia syndrome (EMS) from a 1989 contaminated manufacturing batch — strong evidence. This is well documented: over 1,500 cases and dozens of deaths were traced to a contaminant from a specific manufacturing process change at one Japanese supplier, not to tryptophan itself. It led to a US FDA ban on tryptophan sales from 1991–2001, since lifted with better manufacturing quality controls in place.
Typical dose
Sleep studies have generally used around 1–2 g before bed; mood-related trials have used a wider 0.14–3 g/day range
Upper limit: No formal UL has been established by dietary reference intake bodies for supplemental tryptophan, though the 1989 eosinophilia-myalgia syndrome history is a strong argument for sourcing only quality-tested products
Timing
Often taken before bed, sometimes with a small carbohydrate snack.
Time to effect
- Same night: Sleep-architecture effects (like reduced time awake after sleep onset) have shown up in trials on the night it’s taken.
Common myth
“Turkey makes you drowsy at Thanksgiving because of its tryptophan.” In reality: Turkey’s tryptophan content is similar to chicken and other meats — the post-meal drowsiness is much more likely from the size of the meal, its carb and fat content, and often alcohol.
Food sources
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